This application is the U.S. national phase of International Application No. PCT/GB00/03232, filed Aug. 22, 2000, which designated the U.S., the entire contents of which is hereby incorporated by reference.
1. Field of the Invention
The invention relates to the protection of a fastener primarily during placement through a passage in a plurality of elements where the passage contains a sealing substance.
2. Discussion of Prior Art
A known fastener will now be described with reference to FIGS. 1 and 2 of the accompanying drawings.
A known fastener will now be described with reference to FIGS. 1 and 2 of the accompanying drawings, in which:
FIG. 1 is a schematic cross section of a known pin-tail locking bolt positioned for fastening to sheet elements, and
FIG. 2 is an elevation of the known pin-tail locking bolt of FIG. 1 drawn to a larger scale.
Referring to FIG. 1, it is known for elements such as two sections 10, 12 of an aircraft wing skin to be joined together in a fluid-tight manner. A passage 14 is formed through the skin sections 10, 12, the passage having a countersink 16 in an outer surface of the section 12. The skin sections 10, 12 have a flowable sealant 13 between them and sealant is also applied to the countersink 16.
Looking at FIG. 2, a pin-tail locking bolt 18 comprises a head 20, a shank 22 of diameter d1 and a pin-tail part 24 of diameter d2, where d1 is greater than d2. Towards one end 26 of the pin-tail part 24 arranged furthest from the head 20, a series of annular grooves 28 is provided. Towards the end 30 of the shank 22 spaced from the head, a series of annular grooves 32 is also provided. A point of weakness 34 defined by a reduced cross section is provided between the shank 22 and the pin-tail part 24.
Referring again to FIG. 1, the pin-tail locking bolt 18 is advanced through the passage 14. A pneumatic tool 38 has jaws 40 that receive the grooves 28 of the pin-tail bolt 18 and has a front face 41 that abuts the skin section 10. The jaws 40 then pull hard on the pin tail bolt 18 to clamp the skin sections 10, 12 together. An annular collar 42 is then swaged onto the grooves 32 in the shank 22, for example, by pneumatic devices 44. Continued pulling on the pin-tail bolt 18 by the pneumatic tool 38 eventually breaks the pin-tail part 24 away from the shank 22 of the installed bolt 18, at the point of weakness 34. However, as the pin-tail bolt 18 is advanced through the passage 14, sealant 13 squeezed into the passage 14 from between the skin sections 10, 12 and excess sealant applied to the countersink 16 is picked up by and contaminates the grooves 28. It is conventional to clean the pin-tail bolt 18 and particularly the grooves 28, with a rag prior to applying the pneumatic tool 38. However, such a cleaning operation is not efficient and the pneumatic tool 38 generally becomes contaminated by the sealant which is undesirable.
An aim of the invention is to protect the fastener against such contamination.
According to a first aspect of the invention there is provided a sheath for protecting a fastener as it is passed through a passage, the sheath defining a first hollow at a first end for receiving part of a fastener and a second hollow at a second end suitable for collecting a substance in the passage.
In that way, when the sheath-covered fastener passes through a passage occupied, say, by sealant, the first end of the sheath protects the fastener from contamination by the sealant whilst the second end of the sheath can collect sealant.
The sheath can be removed from the fastener after passing through the passage to expose the part of the fastener which is clean.
Preferably, the sheath further comprises an internal barrier to prevent sealant which enters the second hollow making contact with the fastener.
The barrier is preferably an internal wall, most preferably a bulkhead.
The sheath is preferably of circular cross sectional shape.
The sheath may be provided with at least one rib on its outer surface. The or each rib is preferably in the form of a circumferential projection, for example of annular form. The rib arrangement is useful for wiping sealant from the surface of the passage as the sheath passes there through.
Preferably the or each rib has a radially outer surface of convex cross-sectional shape.
Preferably, there are at least two ribs on the outer surface of the sheath.
According to a second aspect of the invention there is provided a sheath according to the first aspect of the invention or any of the consistory clauses relating thereto with a fastener therein.
The sheath is preferably a push or sliding fit on the fastener. Preferably, the fit is such that sealant is unable to pass between the sheath and that part of the fastener therein.
Where the barrier is provided, the fastener may abut the barrier. In that way, the barrier will provide a surface against which the fastener abuts to push the sheath through a passage.
Preferably, the part of the fastener within the sheath has grooving thereon.
Preferably, the fastener is a bolt and most preferably, a pin-tail locking bolt. In the latter case, the sheath preferably receives the pin-tail part of a pin-tail bolt. In that way, the pin-tail part remains protected from contamination by the sealant.
Where the pin-tail part of a locking bolt is of a lesser diameter than the main body of a pintail locking bolt, the sheath is preferably of a thickness that makes the pin-tail part with the sheath thereon similar in diameter to that of the main body thereby enabling the sheath to fit over the pin-tail part and still pass through the passage for which it is intended.
According to a third aspect of the invention there is provided a method for protecting a fastener during movement through a passage having a substance therein from which part of the fastener is to be protected, the method comprising the steps of, positioning the said part of the fastener within a sheath, advancing the fastener and the sheath through the passage such that the sheath shields the said portion of the fastener from contamination by the substance in the passage, and then removing the sheath from the fastener.
Preferably, the method comprises providing the fastener in the form of a bolt, most preferably a pin-tail locking bolt.
In the latter case, the method may comprise the step of fitting the sheath on the pintail part of the bolt.
Preferably, the method comprises forming the passage in a plurality of elements such as skin panels for an aircraft.
The sheath may be of greater length than the passage.